1. Technical Field
The present invention relates generally to a scanning probe microscope and, more particularly, to a scanning probe microscope that measures information on various physical properties of a sample, such as a surface shape, viscoelasticity or the like, in such a manner as to bring a probe near to a surface of the sample to scan the sample.
2. Description of the Related Art
As well known to those skilled in the art, a scanning probe microscope (SPM) measures a surface shape of a sample in such a manner as to bring a probe attached to a front end of a cantilever near to or in contact with a surface of the sample. A scanning probe microscope in which an optical lever method of radiating a laser beam to a rear surface of a front end of a cantilever to detect a reflected beam is adopted is known as such a scanning probe microscope. According to the optical lever method, a dislocation of the reflective beam of a beam radiated to the cantilever is detected as a displacement of the cantilever, and the surface of the sample is scanned such that a displacement amount of the cantilever is feedback-controlled to be uniformly maintained. Furthermore, physical properties such as a surface shape, viscoelasticity or the like of the surface of the sample can be measured by setting a feedback controlling signal as information on the physical properties.
However, when such an optical lever method is used, the ┌adjustment of an optical axis┘ is needed such that a position of a laser beam or a detector is adjusted so that intensity of a reflective beam reflected from the cantilever becomes the highest. Thus, a technology for guiding laser beams emitted from a side to a lower portion using a beam splitter and radiating the laser beams to the cantilever by installing an optical microscope and a video camera just above the cantilever, and disposing the beam splitter on an optical axis of the optical microscope has been developed (Patent Document 1). According to this technology, the adjustment of the optical axis can be easily carried out because some of the laser beams are headed for upwards via the beam splitter, and a position of the laser beams can be directly confirmed by the optical microscope.
In addition, a measurement site of the optical microscope is needed to be specified before measurement of the sample. Thus, the applicant has developed a technology for disposing an optical microscope at a position corresponding to an upper portion or a lower portion of a cantilever and slantingly radiating a laser beam so that the laser beam is not radiated to the optical microscope (Patent Document 2). According to this technology, since a reflective part changing a path of the laser beam is disposed beyond a visual field of the optical microscope, observation of the sample can be clearly carried out using the optical microscope.